Solution conformations of early intermediates in Mos1 transposition

DNA transposases facilitate genome rearrangements by moving DNA transposons around and between genomes by a cut-and-paste mechanism. DNA transposition proceeds in an ordered series of nucleoprotein complexes that coordinate pairing and cleavage of the transposon ends and integration of the cleaved ends at a new genomic site. Transposition is initiated by transposase recognition of the inverted repeat sequences marking each transposon end. Using a combination of solution scattering and biochemical techniques, we have determined the solution conformations and stoichiometries of DNA-free Mos1 transposase and of the transposase bound to a single transposon end. We show that Mos1 transposase is an elongated homodimer in the absence of DNA and that the N-terminal 55 residues, containing the first helix-turn-helix motif, are required for dimerization. This arrangement is remarkably different from the compact, crossed architecture of the dimer in the Mos1 paired-end complex (PEC). The transposase remains elongated when bound to a single-transposon end in a pre-cleavage complex, and the DNA is bound predominantly to one transposase monomer. We propose that a conformational change in the single-end complex, involving rotation of one half of the transposase along with binding of a second transposon end, could facilitate PEC assembly

Sélecteur mécanique de neutrons lents

A mechanical selector of slow neutrons is described. It uses selection by timeof-flight between two wheels.On décrit un sélecteur mécanique de neutrons lents qui utilise la sélection par temps-de-vol entre deux roues

Sélecteur mécanique pour neutrons lents

A mechanical selector of slow neutrons is described. It is constructed of two rotors (diameter 1 m) separated by 1 meter distance. The rotation speed is 6 000 r. p. m. The width of the line obtained is— in the best conditions— 50 μs. Mechanical problems encountered during the construction are analyzed.On décrit un sélecteur mécanique de neutrons lents. Ce sélecteur est constitué de deux rotors distants de 1 mètre, et faisant 1 mètre de diamètre, tournant à 6 000 tours/minute. La largeur de la raie obtenue est, dans les meilleures conditions, de 0,2 Å et la durée de l'impulsion des neutrons de 50 μs. Les problèmes mécaniques rencontrés lors de la construction sont analysés

A neutron investigation of yeast valyl-tRNA synthetase interaction with tRNAs.

A new way of studying RNA-protein complexes, using neutron small angle scattering in solution, is described and was applied in the case of the system, yeast valyl-tRNA synthetase, interacting with its cognate and non cognate yeast tRNAs. It was shown that, when limited amounts of tRNA (either cognate or non cognate) are added to valyl-tRNA synthetase, a complex consisting of two enzyme molecules and one tRNA molecule is first formed. It is subsequently dissociated to a one to one complex when more tRNA is present in the solution. The association curve shows a maximum for a molecular ratio, enzyme over tRNA, equal to 2

Etude des caractéristiques d'une cavité laser en X de forte puissance

This study is devoted to a new ring cavity, an X geometry. It allows to obtain about 280 W in opposite to the 450 W of the initial linear cavity. The difference in the values comes from the formation of an instable cavity due to the length of the cavity which is longer. Expecting that, the quality factor of the beam is lower for the X configuration and consequently power density are higher and cutting speed are 50 % greater than for the linear system. Concerning welding, due to the higher level of power density, the key hole is more easily formed than with the linear configuration and the penetration increases. So, even if the optical way is difficult to adjust, cutting and welding performances are interesting.Cette étude est relative à une nouvelle cavité en anneau, avec une géométrie en “X”. Elle permet d'obtenir un faisceau de meilleure qualité que lorsque la cavité est sous forme linéaire, et par suite les puissances spécifiques peuvent être multipliées par un facteur 10 au moins. Ce gain, qui se fait au détriment de la puissance moyenne maximale délivrable (75 % de celle atteinte avec la configuration linéaire) reste intéressant car les vitesses de découpe et de soudage en faibles épaisseurs sont augmentées d'environ 50 %